package openapi

import (
	"fmt"
	"os"
	"strings"
	"testing"

	"go.yaml.in/yaml/v4"
)

var httpOperationMethods = map[string]struct{}{
	"delete": {}, "get": {}, "head": {}, "options": {},
	"patch": {}, "post": {}, "put": {}, "trace": {},
}

func TestOpenAPIDocumentsHaveClosedContracts(t *testing.T) {
	for _, name := range []string{"proxy-pool.yaml", "admin.yaml"} {
		name := name
		t.Run(name, func(t *testing.T) {
			root := readOpenAPIRoot(t, name)
			validateLocalReferences(t, root)
			validateOperations(t, root)
			validateSecurityRequirements(t, root)
		})
	}
}

func validateLocalReferences(t *testing.T, root map[string]any) {
	t.Helper()
	walkOpenAPI(root, func(path string, value any) {
		object, ok := value.(map[string]any)
		if !ok {
			return
		}
		reference, exists := object["$ref"]
		if !exists {
			return
		}
		text, ok := reference.(string)
		if !ok || !strings.HasPrefix(text, "#/") {
			t.Errorf("%s has unsupported reference %v", path, reference)
			return
		}
		if _, ok := resolveLocalReference(root, text); !ok {
			t.Errorf("%s points to missing local reference %q", path, text)
		}
	})
}

func validateOperations(t *testing.T, root map[string]any) {
	t.Helper()
	paths, ok := root["paths"].(map[string]any)
	if !ok || len(paths) == 0 {
		t.Fatal("paths must be a non-empty object")
	}
	operationIDs := make(map[string]string)
	for path, rawItem := range paths {
		item, ok := rawItem.(map[string]any)
		if !ok {
			t.Errorf("path %q has type %T, want object", path, rawItem)
			continue
		}
		for method, rawOperation := range item {
			if _, ok := httpOperationMethods[strings.ToLower(method)]; !ok {
				continue
			}
			operation, ok := rawOperation.(map[string]any)
			if !ok {
				t.Errorf("%s %s has type %T, want object", method, path, rawOperation)
				continue
			}
			operationID, _ := operation["operationId"].(string)
			if strings.TrimSpace(operationID) == "" {
				t.Errorf("%s %s has no operationId", method, path)
			} else if previous, duplicate := operationIDs[operationID]; duplicate {
				t.Errorf("operationId %q is shared by %s and %s %s", operationID, previous, method, path)
			} else {
				operationIDs[operationID] = method + " " + path
			}
			responses, ok := operation["responses"].(map[string]any)
			if !ok || len(responses) == 0 {
				t.Errorf("%s %s has no responses", method, path)
			}
		}
	}
}

func validateSecurityRequirements(t *testing.T, root map[string]any) {
	t.Helper()
	components, _ := root["components"].(map[string]any)
	schemes, _ := components["securitySchemes"].(map[string]any)
	walkOpenAPI(root, func(path string, value any) {
		if !strings.HasSuffix(path, ".security") {
			return
		}
		requirements, ok := value.([]any)
		if !ok {
			t.Errorf("%s has type %T, want array", path, value)
			return
		}
		for _, rawRequirement := range requirements {
			requirement, ok := rawRequirement.(map[string]any)
			if !ok {
				t.Errorf("%s contains %T, want object", path, rawRequirement)
				continue
			}
			for name := range requirement {
				if _, exists := schemes[name]; !exists {
					t.Errorf("%s references unknown security scheme %q", path, name)
				}
			}
		}
	})
}

func readOpenAPIRoot(t *testing.T, name string) map[string]any {
	t.Helper()
	payload, err := os.ReadFile(name)
	if err != nil {
		t.Fatalf("read %s: %v", name, err)
	}
	var root map[string]any
	if err := yaml.Unmarshal(payload, &root); err != nil {
		t.Fatalf("parse %s: %v", name, err)
	}
	return root
}

func walkOpenAPI(value any, visit func(string, any)) {
	var walk func(string, any)
	walk = func(path string, current any) {
		visit(path, current)
		switch item := current.(type) {
		case map[string]any:
			for key, child := range item {
				walk(joinOpenAPIPath(path, key), child)
			}
		case []any:
			for index, child := range item {
				walk(fmt.Sprintf("%s[%d]", path, index), child)
			}
		}
	}
	walk("$", value)
}

func resolveLocalReference(root map[string]any, reference string) (any, bool) {
	var current any = root
	for _, token := range strings.Split(strings.TrimPrefix(reference, "#/"), "/") {
		token = strings.ReplaceAll(strings.ReplaceAll(token, "~1", "/"), "~0", "~")
		object, ok := current.(map[string]any)
		if !ok {
			return nil, false
		}
		current, ok = object[token]
		if !ok {
			return nil, false
		}
	}
	return current, true
}

func joinOpenAPIPath(parent, child string) string {
	if parent == "" {
		return child
	}
	return parent + "." + child
}